Heretofore, there has been widely known a motor vehicle in which an engine constituting a power unit is disposed in a front region of a vehicle body, and drive power of the engine is transmitted to a rear differential module and others disposed in a rear region of the vehicle body via a propeller shaft disposed along a frontward-rearward direction of the vehicle body, such as a four-wheel-drive type or so-called FR (front-engine, rear-wheel drive) type motor vehicle.
Generally, a motor vehicle is designed such that, in the event of a collision where an impact force is transmitted in a frontward-rearward direction of a vehicle body, for example, a frontal collision, the impact force is absorbed by allowing a front region of the vehicle body to be crushed or collapsed, while allowing an engine disposed in the front region of the vehicle body to be displaced rearwardly. Although the above motor vehicle having a power transmitting shaft such as a propeller shaft is also designed to allow the front region of the vehicle body to be collapsed while allowing the engine to be displaced rearwardly, the rearward displacement of the engine is apt to be hindered, because the engine is supported from a rear side thereof by the propeller shaft (in a braced state). Thus, in this type of powertrain system, various efforts have been made to relax the braced state which would otherwise be caused by the propeller shaft during a collision.
For example, the following Patent Document 1 discloses a powertrain system which comprises a propeller shaft having a first shaft and a second shaft coupled together through an intermediate joint, wherein the propeller shaft is adapted, when an external force is applied in an axial direction thereof, for example, during a collision in a frontward-rearward direction of a vehicle body, to be axially contracted in such a manner that a distal end of the second shaft is fitted into a base end of the first shaft. In the powertrain system disclosed in the Patent Document 1, based on the axial contraction of the propeller shaft, an engine can be displaced rearwardly by just that much, so that it becomes possible to relax the braced state.
The following Patent Document 2 discloses a powertrain system which comprises an engine provided in a front region of a vehicle body, a differential module provided in a rear region of the vehicle body, and a propeller shaft for transmitting drive power of the engine to the differential module. The differential module has a front support section and a rear support section which support a front portion and a rear portion thereof to the vehicle body, respectively. The front support section is adapted to be broken during a frontal collision, and the rear support section is adapted to support the differential module in a swingable manner during the collision. In this powertrain system, an impact load input into the propeller shaft during a frontal collision causes breaking of the front support section of the differential module to which the propeller shaft is couple, and, upon the breaking, the front portion of the differential module is swingably moved downwardly, so that it becomes possible to relax the braced state which would otherwise be caused by the propeller shaft.